It is the overall goal of this investigation to gain new insights into processes that regulate expression of calcium channels. A fundamental hypothesis is that physiological processes alter calcium channel expression and thereby have a long term modulating effect on excitation-contraction coupling in heart. Little is known about the signalling pathways or the molecular and cellular effectors that determine the number of ion channels a cell will express. Very little is known about how these multimeric proteins are assembled in the cell membrane. It is important to gain an understanding of these fundamental regulatory processes. There is growing evidence that ion channel expression is altered by physiological processes such as development and innervation, and in pathophysiological processes including hypertrophy and heart failure. This project will focus on the L- type calcium channel in rat myocytes. A calcium-dependent and a growth factor dependent signalling pathway will be examined. Specific Aim 1 will test the hypotheses that expression of the alpha 1 subunit of the calcium channel is under transcriptional control, that the turnover rate for the protein in the sarcolemmal is on the order of days, and that there is close correspondence among levels of mRNA, alpha 1 subunit protein, ligand binding sites, and whole cell calcium current. Specific Aim 2 will test the hypothesis that increased cytosolic calcium activity stimulates calcium-calmodulin-dependent protein kinase and increases expression of the alpha 1 subunit gene and protein. Specific Aim 3 will test the hypothesis that angiotensin II decreases calcium channel expression in both neonatal and adult cultured ventricular myocytes. In Specific Aim 4, fundamental processes of transcriptional control for calcium channel subunits will be examined by sequencing the promoter region for the alpha 1, alpha 2 -delta, and beta subunit genes and conducting transient transfection experiments with reporter gene constructs. The hypothesis will be tested that transcription of genes for the three subunits is coordinately regulated. Thus, the project will bring together cellular, molecular and biophysical approaches to produce new knowledge of how calcium channel expression is controlled. Gaining new understanding of regulatory mechanisms for ion channel expression is of broad biological importance and will have therapeutic implications.